Many semiconductor devices employ memory, which can be in the form of individual cells, or cells organized into arrays, typically two-dimensional arrays. Latency time for reading a memory cell preferably should be as small as possible.
Several types of memory technology have been employed. One such memory technology is a differential bit cell design. Such a bit cell design employs two current pathways (that is, two sides, which can for instance be in a bistable configuration). For some such designs, at a given time one side is conducting current, and other side is not. The differential bit cell design provides reliability, in that a differential bit cell can be correctly read, even if one of the two sides fails to hold a correct voltage value.
However, if the differential bit cell is regarded as undesirably large, then a smaller bit cell, employing only a single floating gate device per bit, can be a preferable alternative. Such a single-ended memory has only about half as many data lines as the differential bit cell and typically takes less dynamic power (that is, switching power which is related to switching frequency) to read it. Power reduction is due to having half a number of the data lines to pre-charge and discharge during a read operation. The data lines typically run a length of a dense array and connect to bitcells on a logical column. The data lines typically have a lot of capacitance that takes a lot of power to charge and discharge.
Yet a third type of bit cell, called a redundant bit cell, stores data in two memory elements that are programmed to a same state. The data lines for the two memory elements can be shorted together, since the two memory elements always have the same state. The redundant bit cell has most of reliability advantages of the differential bit cell, but with only half the data lines it takes less dynamic power to read it.
Non-volatile memory (NVM) is a memory technology which has provided advantageous reductions in power consumption, relative to other technologies. NVM retains its stored bit value data if power is cycled down, and then backed up. Therefore, the data which is only intermittently accessed can be stored in NVM, with advantageous power savings.
In addition, certain applications for the memory technology make particular requirements. For instance, a radio-frequency identification device (commonly called an RFID tag) will typically include a small amount of information stored in memory cells, and will not have an independent on-board power source. Rather, the RFID tag reader produces an electromagnetic field, which provides power to the RFID tag when it is sufficiently nearby. The power enables a reader to wirelessly read the information in the memory of the RFID tag.